1. Field of the Invention
This invention relates to a device for mouth-inhaling atomized medicaments dispensed by an aerosol can.
2. Discussion of the Background
Inhalation is the preferred system for administering medicaments (such as beta-2-stimulants, beta-adrenergics, antiallergic and anti-inflammatory agents) directed to the deepest parts of the respiratory tree in that it considerably reduces the dose compared with oral administration. It almost completely eliminates systemic side-effects and provides rapid onset of therapeutic action.
For this purpose pressurized cans containing the medicament and a propellant are used, the cans being provided with dispensers which when manually operated dispense measured quantities of atomized medicament through a nozzle.
Because of their ease of handling and the fact that they allow rapid and selective administration of the active principle, these cans have encountered considerable favor and are widely used both in maintenance therapy on chronic obstructive respiratory affections and in the treatment of acute asthmatic attacks.
Notwithstanding their apparent simplicity, common pressurized cans for dispensing measured quantities of aerosol are difficult to use correctly, as is confirmed by much scientific literature which states that most patients use them incorrectly either because they are unable to synchronize the dispensing action with their own inhalation and hence do not inhale the medicament at the correct moment, i.e. at the act of its delivery, which is violent and of very short duration, or because the patient does not maintain an adequate inhalation flow, or does not inhale sufficiently deeply, or for other reasons.
This problem becomes even more important in the case of certain patients such as children, the elderly and patients with reduced respiratory or manual capability.
Even if a dispensing can for aerosol medicaments is used correctly, the availability of an inhaled medicament to the air passages depends largely on the size of the aerosol droplets (propellant droplets covering medicament particles), which is governed by the formulation, and on the propellant evaporation time.
It is in any event well documented that even under the most favorable conditions only 10% of the aerosol dose dispensed by a pressurized can reaches the air passages. A similar percentage is expired or is deposited outside the oral cavity, whereas because of the impact of the high speed particles about 80% is deposited within the oropharyngeal cavity, is swallowed and absorbed at the systemic level (and hence practically lost).
The quantity of medicament inhaled is however usually sufficient to achieve the pharmaceutical effect.
However, if the pressurized can is not used in the appropriate manner the quantity of medicament which reaches the site of action at the pulmonary level is further reduced and the therapeutic response is compromised.
Excessive medicament depositing in the oropharyngeal cavity can also lead to undesirable effects either at the systemic level as a consequence of the medicament absorption, or at the local level, as in the case of corticosteroids, which can result in oral candidiosis. In an attempt to overcome the problems connected with the direct use of cans for dispensing measured quantities of atomized medicament, devices have been developed over the last decade for application to the nozzles of pressurized dispensing cans. Depending on their dimensions these devices can be classified as either "spacers" or actual "expansion chambers".
In practice, the "spacer" devices are tubes to be interposed between the can dispensing nozzles and the mouth of the user to improve the amount of deposition of the medicament at the pulmonary level by intervening on two factors, namely the size of the aerosol droplets and their impact within the orophangeal cavity.
In this respect, the period between the dispensing of the spray and its inhalation allows rapid evaporation of the propellant and a resultant decrease in the size of the particles before they enter the respiratory tree, thus favoring improved penetration as far as the lower air passages.
Again, the space which the "spacer" device interposes between the dispensing nozzle and the patient's mouth facilitates the evaporation of the propellant vapor and decreases the particle speed, so reducing the percentage of medicament lost due to immediate impact with the oral cavity.
Finally, the quantity of inhaled propellant is reduced, with consequent greater pleasantness for the user and a lessening of risks connected with its possible toxicity.
The "spacer" devices of the aforesaid type have the common characteristic of a substantially cylindrical shape and a fairly small volume (70-100 ml).
The use of this type of "spacer" device has rapidly become extensive as an aid to those patients who are unable to properly use the common cans for dispensing measured quantities of aerosol or who have difficulty in understanding the rather complicated instructions.
Evidence from the scientific literature shows however that the addition of small "spacers" does not produce appreciable improvement at the clinical level.
For this reason research in this sector has been orientated towards the perfection of devices in the form of actual large-volume expansion chambers.
Besides possessing the advantages attributed to the "spacer" devices, these "expansion chambers" should contribute to resolving the considerable problem of lack of coordination between the dispensing action and the inhaling action, because they enable the intake to be delayed by a few seconds after delivery, hence aiding patients with more serious respiratory difficulties.
However, known "expansion chambers" have considerable drawbacks which hinder their use and acceptability. In this respect, as the aerosol jet is sprayed into the cavity defined by said chambers, the aerosol droplets strike the chamber walls to then diffuse into the central region of the chambers. A large number of the medicament droplets tend to deposit on the chamber walls and are lost. To reduce this problem, the known "expansion chambers" are of large size (for example about 750 ml), making their portable use practically impossible and creating storage problems for the factory and pharmacy. An expansion chamber of this type is described in GB patent 1,565,029.